不理解 Ruby ljust/rjust/center 方法

我正在学习嵌套，我的任务是使每条新行都以缩进开头。这是我的代码，但它不起作用

$nestingDepth = 0

def logger description, &block
    puts "Beginning #{description}".rjust($nestingDepth)
    puts $nestingDepth
    $nestingDepth = $nestingDepth + 10
    result = block.call
    $nestingDepth = $nestingDepth - 10
    puts $nestingDepth
    puts "End of #{description} block that returned #{result}".rjust($nestingDepth)
end

logger "first block" do 
    logger "second block" do
        logger "third block" do 
            puts "third block part"
        end
        puts "second block part"
    end
    puts "first block part"
end

您的代码有几个问题：

• 您正在使用全局变量，这通常是一个坏主意，请将其作为参数传递下去。为此，您可以使用DSL定义记录器和日志方法的类。
• 你正在打电话puts在块内，但您从未更改它的定义，我不明白您如何期望它打印缩进的字符串，它只会正常打印字符串而无需缩进。为此，您需要定义一个带有缩进打印的特殊方法，例如log
• 你正在打电话rjust期望它会缩进字符串。此方法有不同的目的 - 以指定的长度将字符串向右对齐（即向左填充）。如果字符串超过指定长度，则返回原始字符串。要实际缩进一个字符串，你应该这样做puts ' ' * nestingDepth + string。乍一看很神奇，但*运算符只是重复字符串，例如'abc' * 3 #=> 'abcabcabc'

总的来说，我会这样做：

class DSL
  def initialize
    @depth = 0
  end

  def logger(description, &block)
    log "Beginning #{description}"
    @depth += 1
    result = instance_eval(&block)
    @depth -= 1
    log "End of #{description} that returned #{result}"
  end

  def log(string)
    puts indent + string
  end

  private

  def indent
    ' ' * (10 * @depth)
  end
end

def logger(*args, &block)
  DSL.new.logger(*args, &block)
end

Example:

logger "first block" do 
  logger "second block" do
    logger "third block" do 
      log "third block part"
    end
    log "second block part"
  end
  log "first block part"
end

这打印：

Beginning first block
          Beginning second block
                    Beginning third block
                              third block part
                    End of third block that returned
                    second block part
          End of second block that returned
          first block part
End of first block that returned